A recurrent problem in the medical and surgical intensive care field is the patient with coextensive respiratory and cardiac failure. Patients exhibiting this condition are typically treated through the use of positive pressure ventilation techniques, such as standard volume cycled ventilation, inotropic infusions and not infrequently with mechanical cardiac assist devices such as the intra-aortic balloon pump (IABP) or the ventricular assist device (VAD).
It will be appreciated that inotropic infusions have inherent risks and benefits. While they may improve perfusion, i.e. the movement of fluids, through cardiac and cerebral circulation systems, there may be detrimental effects to perfusion in pulmonary and splanchnic circulation systems.
Unfortunately, devices such as the IABP or VAD necessitate intravascular placement of a foreign body, i.e. surgical implantation, with the attendant risk of infection or vascular injury. Additionally, IABP provides cardiac assistance based on the principal of cardiac cycle-specific changes in the volume and pressure of the proximal aorta through the use of an intra-aortic balloon. When implementing IABP, cardiac afterload is decreased during systole, i.e. ejection of fluid from the heart, by deflating the balloon. Cardiac afterload is that parameter indicative of volume and pressure of the proximal aorta. Deflation of the balloon enhances so-called stroke volume--forward blood flow. Cardiac afterload is increased during diastole, i.e. filling of the heart, by inflating the balloon, thereby enhancing coronary perfusion.
In the present invention, cardiac cycle-specific non-invasive changes in intra-thoracic pressure are used to effectuate changes on ventricular preload and afterload and by direct mechanical action on the myocardium to improve cardiac performance. Studies relating to changes in intrathoracic pressure have been carried out. See M. R. Pinsky et al., Determinants of cardiac augmentation by elevations in intrathoracic pressure, Journal of Applied Physiology, Vol. 58 (4), pps. 1189-1198 (1985) and M. R. Pinsky et al., Hemodynamic effects of cardiac cycle-specific increases in intrathoracic pressure, Journal of Applied Physiology, Vol. 60 (2), pps. 604-612 (1986). However, such studies on laboratory specimens, particularly mongrel dogs, have found that absent the use of constrictive devices such as thoracoabdominal binding, inspiratory jet pulses from a high frequency jet ventilator had minimal hemodynamic effects as evidenced by small changes in pleural pressure. Furthermore, the authors were only able to demonstrate an effect on the failing heart, not on the normally functioning heart. One of the problems associated with these studies is that the thorax of the subject specimens had to be opened and several monitoring devices implanted. Furthermore, these studies concentrated only on the effect of cardiac gated respiration on the heart. It did not evaluate the effect of this modality on ventilation/perfusion relationships in the lungs.
Unfortunately, the unique interactions between the heart and lungs in the negative-pressure environment of the intact thorax have been difficult to study quantitatively. Consequently, these unique interactions have been studied only on a limited basis via non-invasive techniques. Developments in recent years to three-dimensional imaging have gone a long way toward providing satisfactory techniques to non-invasively assess intrathoracic organ geometry and function.
An ultra-fast X-ray computed tomography (CT) scanner has been produced by Imatron Corporation which is capable of acquiring two (2) slices of the body every 50 ms. By combining such a CT scanner together with equipment to focus the scanner on particular physiologic conditions, non-invasive data relating to precise physiologic conditions can be gathered. When such data is interrogated utilizing new software packages, post analysis of the 4-dimensional data sets can be achieved. One such package is the VIDA.TM. imaging software developed at the Cardiac Imaging Research Center, Department of Radiology at the Hospital of the University of Pennsylvania. Utilizing such equipment, non-invasive studies of the thorax are possible which may prove beneficial to patients experiencing either cardiac failure alone, respiratory failure alone or a combination of cardiac and respiratory failure.
A need exists for apparatus and/or methods for treating cardiac and/or respiratory failure which apparatus and methods are non-invasive in relation to the thorax, whereby cardiac and/or respiratory function are not diminished in the process of augmenting one system or the other.